Semiconductor magnetic field sensors are devices sensitive to a magnetic field (H) or to a magnetic induction (B). Semiconductor magnetic field sensors are often implemented in automotive applications, because magnetic fields penetrate easily through most materials. Semiconductor magnetic field sensors are used in a variety of applications such as brushless-DC motors, angular sensors, current sensors, engine and transmission sensors, ABS (Anti-lock Braking System) sensors, magnetic parking sensors, etc. for improving comfort and safety.
Semiconductor magnetic field sensors may be sensitive to magnetic fields perpendicular or parallel to a plane of a semiconductor chip. The semiconductor magnetic field sensors sensitive to magnetic fields parallel to the plane of the chip may be more attractive for practical use because the magnetic field sensitive structures may be placed at different angles on the surface of the semiconductor chip for sensing magnetic fields at different directions of the chip plane.
Semiconductor magnetic field sensors based on lateral structures may be of different types. They may be: (a) bipolar magnetotransistors (MTs), consisting of two or more collectors and at least one emitter somewhere in between the collectors; (b) magnetodiodes (MDs), consisting of two or more current-collecting contacts (collectors) and at least one current-emitting contact (emitter) somewhere in between the collectors; (c) magnetoresistors (MRs), consisting of two or more current collecting contacts (collectors) and at least one current-emitting contact (emitter) somewhere in between the collectors. Magnetodiodes (MDs) and magnetoresistors (MRs) have no base region, nor base contacts, such as present in magnetotransistors (MTs).
Many semiconductor magnetic field sensors suffer from the imperfections with which they are fabricated. These imperfections may be caused by material asymmetries (e.g. not uniform doping of the silicon, presence of impurities or crystal defects).
In most (modern) semiconductor technologies special integrated features are provided to prevent current leakage between two adjacent semiconductor device components. These features are best known as Shallow Trench Isolations (STI). Shallow trench isolations are manufactured early during the semiconductor device fabrication by etching a part of the silicon, growing first a thin layer of a dielectric material (e.g. silicon dioxide or silicon nitride) and subsequently depositing a thicker layer of the dielectric material to fill the etched part (so-called trench). While these STI are particularly advantageous in isolating semiconductor device components from each other and in reducing the effect of parasitic coupling, STI may be one of the causes of material asymmetries in the fabrication of semiconductor magnetic field sensors. These imperfections cause an offset in the detection of magnetic fields (e.g., a semiconductor magnetic field sensor would give a non-zero output in the absence of a magnetic field). This offset degrades the accuracy of the semiconductor magnetic field sensors and needs to be compensated with additional calibration circuitry.
In addition to offset, lateral semiconductor magnetic field sensors might also suffer from low sensitivity problems. Sensitivity in lateral semiconductor magnetic field sensors is a measure of the response of a lateral semiconductor magnetic field sensor to an applied magnetic field (H) or magnetic induction (B). A lateral semiconductor magnetic field sensor with higher sensitivity is desirable because it is able to respond to a smaller applied magnetic field (H) or magnetic induction (B) with better accuracy.
GB2126009A discloses a semiconductor magnetic field sensor comprising a lateral bipolar magnetotransistor having only one single emitter region and a base region. The base region is heavily doped with impurity atoms, and is incorporated in the surface of a silicon substrate that is lightly doped with impurity atoms. The emitter region, collector regions and the base region of the magnetotransistor are adjacently aligned. This magnetotransistor suffers of low sensitivity because of a parasitic current that is lost through the lightly doped substrate and cannot be deflected by the magnetic field.